1. Field of the Invention
The present invention relates to disk devices in which error-correction processing is performed when an error occurs during reading of data from disks.
2. Description of the Related Art
FIG. 4 illustrates error-correction processing performed by a conventional disk device.
A disk device shown in FIG. 4 is used for reading data from and writing data to a conventional flexible disk. A disk drive 10 and a host computer 30 are connected by a predetermined interface. The disk drive 10 loads a disk 16 having a predetermined format in a disk drive body 14. The host computer 30 includes an operating system (OS) 31 and a device driver 32 for controlling the disk drive body 14. Data delivery is performed between the disk drive body 14 and the OS 31 by means of the device driver 32.
An error-correction code (hereinafter referred to as an “ECC”), such as a C1 code of Reed Solomon codes, is added along with data itself to a signal written to the disk 16 for every sector. Error correction is performed by reading and processing the ECC when reading data.
The conventional disk device is provided with an error-correction unit on a processing circuit of the disk drive 10. Using the ECC, such as the C1 code, read from the disk, the error-correction unit in the disk drive 10 performs error correction in units of one block (physical block address; PBA) corresponding to data in one sector.
A flexible magnetic disk for high-density storage with a capacity of, for example, approximately 200 MB, has a substantially smaller track width than a conventional disk due to increased writing density. The disk for high-density storage has a much higher writing frequency. When an error occurs in read data due to a defect or dirt on the surface of the disk, the size of the region influenced by such a defect or dirt is substantially increased, so as to extend over a plurality of sectors. In such a case, an error may not be recovered by error correction in data units (PBA units) for one sector based on the ECC, such as the C1 code.
It has therefore been proposed to provide a hardware error-correction unit having an error correction capability higher than the above error-correction unit. In order to provide such an error-correction unit, a CPU contained in the disk drive 10 must be replaced by one with a greater operational capacity. It is also necessary to increase the memory capacity. Thus, an electronic circuit installed in the disk drive 10 must be very expensive.